1. Field of the Invention
The present invention relates to a control device of an internal combustion engine, the control device that determines whether or not to perform sensor element heating control of an air-fuel ratio sensor based on the mass of condensed water that develops in an exhaust pipe.
2. Description of the Related Art
JP-A-2009-228564 discloses the technology to compute the mass of condensed water by map-computing the condensed water integrated quantity based on a relative wall temperature which is a difference between an estimated exhaust pipe temperature and the dew point and an exhaust gas mass flow rate and adding the condensed water integrated quantity to a previous value in a control device of an exhaust gas sensor, the control device that controls the energization state of a heater that heats the exhaust gas sensor provided in an exhaust pipe of an internal combustion engine. The condensed water integrated quantity map is set so that the mass of condensed water is decreased as the relative wall temperature rises and the condensed water integrated quantity takes a negative value when the exhaust gas mass flow rate is more than or equal to a reference value. The technology to permit the energization of the heater that heats the exhaust gas sensor when it is determined that no condensed water is present in the exhaust pipe based on the computed mass of condensed water is disclosed.
However, after the internal combustion engine is started, a large part of the period in which the condensed water is present in the exhaust pipe is an evaporation process in which the exhaust pipe is above the dew point, and, since transfer of mass and energy between the exhaust gas and the condensed water is an important factor during the evaporation process, it is impossible to compute the amount of condensed water with high accuracy based only on the relative wall temperature and the exhaust gas mass flow rate.
Therefore, when the heater is started at a time point earlier than an original time point at which the condensed water disappears completely, a crack appears in the sensor element due to immersion in water. On the other hand, when the heater is started at a time point later than a time point at which the condensed water disappears completely, a reduction in the accuracy of air-fuel ratio control at start-up causes a decrease in exhaust performance.